Water supply and history: Harappa and the Beas regional survey

Abstract

Introducing the methods of archaeoclimatology, the authors measure the relative locus of the monsoons, the intensity of winter rains and the volume of water in the rivers in the Upper Indus, in the region of Harappa. They also note the adoption of a multi-cropping agricultural system as a possible strategy designed to adjust to changing conditions over time. They find that around 3500 BC the volume of water in the rivers increases, and the rivers flood, implying annual soil refreshment and the consequent development of agriculture. By contrast, from around 2100 BC the river flow begins to fall while the winter rains increase. This time-bracket correlates nicely with the brief flourishing of Harappa. The locally derived evidence from Harappa combined with the Beas survey data provide a model for understanding the abandonment of settlements in the Upper Indus and possibly the wider civilisation.

Fluvial landscapes of the Harappan civilization

“…An intense drought period around 4,200 y ago, linked to major disruptions in Egypt and Mesopotamia (53)(54)(55)(56), coincides instead with the flourishing of Harappan urbanism within the limits of available chronology. This event, recorded at the start of the aridification process in South Asia, had affected the total Indus discharge (57), but aridification may have diminished the intensity of floods and allowed inundation agriculture to expand along the Indus and its tributaries (20). However, our analysis of fluvial landscapes suggests that further drying was detrimental for the Harappans, who relied on annual floods to sustain their economy.…”

“…Alternatively, environmental factors were suggested to play a decisive role in the decline (1,2,8); among these, regional aridification, hydrological changes such as the drying or capture of the Ghaggar-Hakra system (3,4,7,19,20), as well as human-induced environmental degradation (21) have been advanced. Despite almost a century of research, a clear perspective on the role played by fluvial dynamics in influencing the fate of the Harappan civilization has been hampered by a lack of high-resolution topographic data and sedimentary chronologies.…”

“…In this context, however, the preferential occurrence of Harappan urban sites on interfluves, but in close proximity to floodable, agriculturally viable land (20,24), suggests awareness of devastating floods that can occur on Himalayan rivers. Settling of the Ghaggar-Hakra river system is the best example of an adaptation strategy that takes advantage of smaller floods along monsoonal rivers, where monsoon rains are not augmented by meltwater.…”

“…As during the Harappan era (7,10,20), inundation agriculture during the Rabi season (winter crops) was dominant along the Indus and its tributaries (10,38, SI Text) prior to the development of the largest irrigation system in the world in 20th century Pakistan. Hydroclimate reconstructions for South and Central Asia (39)(40)(41) show that precipitation from both monsoon and westerly sources that feed rivers of the western Indo-Gangetic Plain (20) decreased since approximately 5;000 y ago, and was at its lowest after approximately 4;000 y BP (Fig. 4).…”

Historical and Technical Notes on Aqueducts from Prehistoric to Medieval Times

“…2800-2600 BC, Harappa grew from a small town to a major city (approximately 150 ha in 2600 BC). In approximately 1900 BC, Harappa's infrastructure began to deteriorate, although the city was not abandoned until possibly as late as 1300 BC [17].…”